Digitally coded communication signals are used in certain wireless communication systems. One such system is a Code Division Multiple Access (CDMA) cellular system. In a typical CDMA system, digitally coded communication systems signals are transmitted in a common channel between a mobile station and a base station. In a typical CDMA system, multiple communication channels of a fixed bandwidth are used to handle communications with mobile units.
In order for a base station to support the reception of multiple communication channels, a separate receiver is provided for each of the communication channels. In a typical embodiment, each receiver includes a filter to isolate the channel of interest. However, providing a receiver for each communication channel increases the size and cost of base stations.
Additionally, signals received by base station are subject to interference from a variety of sources. In order to ensure proper reception of communication signals, base stations must be able to handle the interference while receiving the communication signals. In the CDMA standards for base stations, a base station needs to be able to process communication channels that are subject to one or two interferers. The interferers are signals of high signal strength located near a communication channel. In a typical CDMA system utilizing separate receivers for each communication channel, this requirement is easily satisfied by filtering out the interfering signals. One drawback of current systems is that base stations must have a receiver for each communication channel supported by the base station. This increases both the size of the base station and the cost to deploy the base station.
To decrease the size and cost of base stations, wideband receivers have been proposed that can receive and process several common channels. These receivers typically utilize an analog-to-digital converter (ADC) to convert the received analog signal to a series of digital values, before separating the signal into individual channels for further processing. However, because the interferers are not filtered out before processing in the ADC, the incoming signal may be of such strength that the maximum capability of the ADC is exceeded and the ADC becomes saturated, which results in the inability to reflect further increases in incoming signal strength as increases in the ADC output. In order to ensure the ADC is not saturated, the incoming signal should be attenuated. Therefore, what is needed is a digital wideband automatic gain control method and device.